A Beginner`s Guide To Speakers

April 20, 1990|By Rich Warren.

The speaker is the most important component in your stereo system. Multithousand-dollar amplifiers and CD players justify their price only through great speakers.

When you assemble a component stereo system, budget at least a third to a half of your investment for speakers. The knobs and flashing lights on your receiver can`t compete with the homely speaker when it comes to determining the ultimate sound of your stereo.

Speaker designers face a more formidable challenge than their colleagues who design electronics. Speaker designers continuously confront the rather rigid laws of physics. Acoustical laws tend to bend more slowly than the physics that governs electronics. Thus speakers evolve more gradually than other components.

While not everything about speakers is written in stone, a lot is carved in wood. About 90 percent of the speakers on the market come enclosed in a wooden box. The remaining 10 percent range from honeycombed aircraft aluminum to concrete.

In reality, what most people think is wood is actually a mix of sawdust and glue known as particle or composite board. This is overlaid with vinyl, wood veneer or lacquer to improve appearance. Besides being too expensive, most varieties of solid wood resonate too much. The less resonance the better. Different companies use varying densities and qualities of particle board for enclosures. The best have the least resonance. A few adventurous designers forge cabinets from more exotic materials, with equally exotic prices.

Similarly, about 90 percent of speaker enclosures are square or rectangular. The remainder would fill a geometry book. Round, pentagonal and flat designs are among the many offering varying justification for forsaking the box.

However, as companies such as B&W, KEF and MB Quart prove, a box works extremely well when properly designed. For example, B&W employs a unique internal bracing system, known as Matrix, that virtually stops the box from resonating. Quart uses multiple layers of high-density particle board forming an unusually thick enclosure.

Thus far, we`ve been using the word speaker to denote the complete system. Most people also use speaker to refer to the components of the system, such as the woofer, midrange and tweeter. Technically, these are referred to as drivers.

The names describe the function: The woofer woofs the bass notes, the midrange fills the middle, and the tweeter tweets the treble. Actually, a well-designed system shouldn`t sound like it`s woofing or tweeting, so accept the names as poetic license.

Most speakers with more than a single driver contain an invisible component: the crossover network, also known as the dividing network. This can be as simple as a single capacitor in a cheap speaker, or a complex array of coils, capacitors and resistors in more expensive speakers.

As the name(s) imply, the crossover or dividing network divides the incoming signal, crossing it over at the correct frequency from the woofer to tweeter. Some speakers include a switch allowing you to adjust the amount of signal going to the tweeter and/or midrange in order to vary the tonal balance.

The crossover protects the tweeter. Bass frequencies contain far greater amounts of energy than the tweeter can handle. If the entire amplifier output reached the tweeter, the delicate coil of wire inside the speaker would melt. While the big woofer with its thicker coil can accept the extra power, treble frequencies confuse it. The woofer is designed to move large quantities of air at a relatively leisurely pace when compared with the tweeter. Too much high-frequency energy distracts the woofer from its job of producing bass, resulting in distortion. Crossovers in cheap speakers often serve only to protect the tweeter, while leaving the woofer to fend for itself.

Stereo salespeople add razzle-dazzle to their pitch by describing the acoustic principle of the enclosure. To entice you to buy their acoustic solution, they talk about acoustic suspension. To tickle your reflex to spend, they describe bass reflex, also known as a ported design. Less common enclosures may incorporate a folded-horn or labyrinth design.

New designs based on some of these older principles from the Bose Corp. include the Acoustic Wave and Acoustimass systems. MB Quart managed to combine the best attributes of acoustic suspension and bass reflex with its Moving Control System (MCS).

Speaker enclosure designs enhance bass with minimal effect on the treble. A well-designed enclosure dramatically aids the woofer in producing not just low bass but accurate bass. Enclosure design tends to be more crucial with smaller speakers, such as bookshelf models.